Osteopontin is a cytokine; Lorenzen et al measured levels in 95 people with idiopathic pulmonary arterial hypertension, 25 of whom were followed prospectively for 3 months after therapy initiation. Elevated osteopontin was more common in people with IPAH than in healthy controls, predicted mortality, and correlated with 6-minute-walk distance and NYHA class in the retrospective cohort. CHEST 2011;139:1010-1017.